INTRODUCTION. 411 



James Hall, in 1858-1861, extended into the Central Wisconsin dis- 

 trict, I have no means of linowing, since no reports were ever pub- 

 lished, except that on the lead region by Prof. Whitney. The large 

 geological chart of Canada and the northern United States, issued by 

 the Canadian Geological Survey, gives some quite accurate details 

 with regard to the distribution of the Lower Silurian formations of 

 Central Wisconsin, and as these were contributed by Mr. Hall, they 

 would seem to indicate that a good deal of work was done by his sur- 

 vey that was never publisKed. 



Future surveys will, beyond doubt, make farther and more detailed 

 observations than now submitted, points now in doubt will be cleared 

 up, and new generalizations, now unthought of, will be made. 

 Amongst those points that now appear especially to need further in- 

 vestigation, may be mentioned the detailed structure of the Archaean 

 terranes of the northern part of the district, and the question as to the 

 existence of two distinct formations within what is now called the 

 the Potsdam sandstone series, the one resting upon the eroded surface 

 of the other. The first of these can be fully attained only by an ex- 

 haustive traversing of the unsettled regions on foot, the location of 

 every outcrop, and the microscopic examination of all specimens. 

 The Archaean ranges of the Baraboo valley, too, deserve a more de- 

 tailed study, and such a one as can only be given by the most thorough 

 traversing on foot. 



The general arrangement of this report, by geological formations, 

 seems to be the only logical one. A complete arrangement by coun- 

 ties involves a great deal of repetition, and renders a report far less 

 intelligible to those outside the state. ^Nevertheless, it has not been 

 thought best to carry the geological arrangement too far, and the local 

 details are, therefore, arranged geographically, so that information 

 with regard to any particular locality may be the more readily found. 

 Moreover, in giving details with regard to the several Silurian forma- 

 tions, these have been grouped together, because in much of the dis- 

 trict the areas occupied by them are so interwoven that any attempt 

 to give the details with regard to each separately would result only in 

 confusion. It is a matter of great regret, to me at least, that the 

 small space necessarily assigned to this report has rendered it impos- 

 sible to print all of the manuscript prepared. The pages thrown out 

 include a detailed topographical and geological description, by town- 

 ships, of most of the Silurian portion of the district; and the plan of 

 the report is marred by the omission. An Appendix on Artesian 

 Wells and a Chemical Appendix, in which are tabulated, with addi- 

 tions, the analyses cited in the following pages, for the most part the 

 work of Mr. E. T. Sweet, are also crowded out. 



